This invention relates to processes for irradiating and grinding PTFE to reduce the molecular weight and render the material grindable to a fine particle powder, which can be used as a dry lubricant in paint and ink.
An early description of irradiation of PTFE is contained in U.S. Pat. No. 3,766,031 to Dillon. According to this patent material was placed in trays and subjected to irradiation.
U.S. Pat. Nos. 4,748,005 and 4,777,192, which are owned by the assignee of the present invention, discloses commercial batch processing of PTFE wherein, the material is placed in a ribbon blender and wherein electron beam radiation is directed into a portion of the blender while the material is agitated by the blender. The blender is provided with cooling either by a water jacket or by direct injection of water into the vessel. The ribbon blender is operated to continuously move the material into and out of the irradiation zone, thereby to achieve uniform irradiation.
U.S. Pat. No. 5,149,727 discloses a processing vessel which includes two vessel portions, each having a paddle blender agitator. Air is injected into the process material to promote cooling, coupled with simultaneous irradiation and grinding. An air classifier is used to draw airborne fine particle PTFE from the vessel for recovery. U.S. Pat. No. 5,296,113 discloses a similar system wherein the agitation is provided by use of injected high pressure air, and wherein material in continuously fed to the processing vessel and extracted by an air classifier to achieve a continuous process.
It is an object of the present invention to provide an improved method and apparatus for processing PTFE.